High pressure gear pump



Dec. 17, 1957 E. KORKOWSKI ETAL 2,816,511

HIGH PRESSURE GEAR PUMP Filed Nov. 25, 1952 35 I I, I 9 2 --TI 27 x I7 i 19 29 a 26 I a 23 g l 1/1 25 H a 6 a United. States. Patent HIGH-PRESSURE- GEAR PUMP Eberhard Korkowski, Stuttgart-Feuerbach, and Gustav Schmidt, Stuttgart-Vaihingen, Germany, assignors to Robert Bosch G. in. b. H., Stuttgart, Germany Application Novemb'erZS, 1952, Serial No. 322,398 Claims priority, application GermanyDecember 7, 1951 2 Claims; (Cl; 103-126) This invention concerns a high pressure gear pump having gear wheels which are self-adjusting in the pump casing or housing through. an axial clearance space on both sides of the wheels and through the aid of pressure cushions produced by the medium being pumped. These pressure cushions dispose themselves in the clearance space between the side faces of the gear wheels and the adjacent facesof the pump casing. and function to maintain the gear wheels in a central position between the casing faces, even in the case where the gear wheels have a relatively large axial displacement. The reason for this is that with the axial displacement of a gear wheel towards a side of the casing, the pressure of the medium being pumped rises greatly in the decreasing axial clearance space at this side of'the casing and forces the gear wheel back again to the central position.

In a known type of gear pump this adjustment is obtained by extracting the pressure medium from the outlet side of the pump and feeding it to the side faces of the gear wheels. The effectiveness of this arrangement thus depends on the delivery pressure of the pump; in addition, the hydraulic efficiency of the pump is impaired due to the loss of pressure mediumwhich, in turn, depends onthe delivery pressure and on the extent of the axial andradial play or clearance.

These disadvantages are avoided according to this invention by the fact that the medium which is subjected to high pressure in the spaces between the teeth of the gear wheels during the meshing, of the teeth, is utilized for producing the pressure cushions at the sides of the gear wheels. The so-called high pressure medium, e. g. liquid is created forcibly during operation of the pump and its pressure and quantity are not dependent upon the delivery pressure. Hitherto, it had to be diverted or discharged without being of any specific use. The high pressure of same and pulsating action promotes the automatic adjustment of the gear wheels.

The invention is further described with reference to the accompanying drawings which illustrate one embodiment of the invention by way of example only and in which:

Fig. 1 is a section through the gear pump, and

Fig. 2 is a section taken on the line IIII of Fig. 1.

The casing of the gear pump consists of an upper part 1, a central or intermediate part 2, a lower part 3 and an end plate 4. In the upper and lower casing parts there are formed bearing bores 5 and 6 in which respective shafts 7 and 8 are slidably mounted with slight radial clearance. Shrunk on to these shafts are gear wheels 9 and 10 which fit into corresponding chamber recesses formed in the central casing part 2. This casing part 2 is provided on either side of the point 11, i. e. the region in which the gear wheels are in mesh with one another, with further recesses 12 and 13 (shown in chain dotted lines in Fig. 2). The recess 12 is larger than the recess 13 and communicates with a bore 14 formed in the upper casing part 1, which bore 14 is in communication with the suction pipe line of the pump. The

smaller recess 13 in the central casing part 2 communicates through a bore 15, also formed inthe upper casing-part; with the pressure pipe-or delivery linev of the pump.

The central casing part2 is slightly thicker than the gear wheels 9 and It) so that when the gear wheels are assembled in the casingthey arecapableflof'limited axial play or. movement for example, 0.04 mm. The bearing bores 5 and 6 in the upper and. lower casing parts are bevelled at their ends which face the gear wheels so as to provide annular grooves 16 and 17. The annular grooves 16 in the upper casing part 1 are interconnected by a groove 18 formed in this face of casing part 1, whi'lstthe: annular grooves 17 in the lower casing part 3 are interconnected by a. groove 19 formed in this face of thelower casing part. The grooves Hand 19 extend across the meshing point 11-of the gear wheels.

The shafts 7 and 8 areprovided with longitudinal bores 20 and 21, respectively, which communicate with a common hollow space or chamber 22 in the lower casing part 3. This space or chamber communicates with the suction side of the pump bymeans of a passage which is not shown. The shaft 7 carries claws or dogs 23 on its driving end for engagement with corresponding claws or dogs on a stub shaft 24. This stub shaft is mounted in the end plate 4 by means of 'a ball bearing 25 and has an extension 26 situated in the longitudinal bore 26 of the shaft 7. Extension 26 has an enlarged end portion 27 which constitutes a bearing and which slides on a collar 28 formed in the interior of bore 20. This sliding bearing is situated'in the central plane of the gear wheel-9. In the end .portion27 of the extension 26 there is provided a longitudinal groove 29.

The stub shaft 24 extends through an opening in the end plate. land this opening is closed by means of a sealing ring 31). The outer end of the stub shaft is provided with. aconical part 31 and a securing nut 32. for mounting a driving wheel.

The various casing parts are held together by means of bolts 33, nuts 34, and positioning pins 35.

Only thetorque force of the drive acts on the gear wheelv 9. The transmission of axial forces to gear wheel 9is prevented by the longitudinally displaceable connection of the shaft 7 with the stub shaft 24, whilst tilting moments are also prevented by mounting the shaft 7 in the long arcuately' fitting bores 5 and 6 and by the central position ofthe collar 28 of shaft extension 26.

When the pump is connected to a system of pipes, which, for example, contain oil, and driven, the pump draws oil through the bore 14, feeds it from the recess 12, with the aid of the spaces between the teeth of the gear wheeis, to the recess 13 and discharges it through the bore 15. Oil is also present between the tooth spaces in the vicinity of the point 11 where the gear wheels are in mesh with one another; the oil is partly enclosed in the tooth spaces and is thus subjected to a relatively high pressure. This high pressure oil escapes on both sides of the gear wheels through the grooves 18 and 19 into the annular grooves 16 and 17. As the clearance spaces between the shafts 7 and 8 and the bores 5 and 6 are small, only a relatively small quantity of the high pressure oil can leak or escape therethrough. This leaking or escaping oil lubricates the sliding bearing surfaces, flows directly through the clearance spaces to chamber 22 or through the bore 20, the groove 29 and the bore 21 into the space or chamber 22, lubricates the ball bearing 25 and returns to the suction side of the pump through the connecting passage which is not shown.

The main quantity of the pressure oil is forced from the annular grooves 16 and 17 between the side faces of the gear wheels 9 and 10 and the adjacent confronting faces of the upper and lower casing parts. The pressure oil in the grooves 18 and 19 on both sides of the gear wheels is equal; if the axial clearance space on both sides of the gear wheels is also equal, then the oil flows along both sides of the gear wheels to the peripheries thereof under equal pressure. If a gear wheel is axially displaced, the axial clearance space is correspondingly decreased on one side so that the pressure of the oil rises greatly on this side as the efilux area is constricted. The pressure on the other side of the gear wheel is correspondingly reduced; the gear wheel which is under the influence of this difference in pressure is again displaced to such an extent that the axial clearance space is equal on both of its sides. The gear wheels are thus prevented from coming into contact with the adjacent faces of the upper and lower casing parts with the result that friction losses are avoided. As experience has proved, the pulsating of the pressure oil occurring at regular intervals, has an accelerating influence on this automatic adjustment or self-centering of the gear wheels. The pressure of the oil remains constant and is independent of the supply pressure, thus enabling the gear wheels to adjust themselves accurately under all operational conditions.

The high pressure oil may also be fed first of all from the point 11 through the passages to the bores 5 and 6 or annular grooves therein, so that from these the oil enters the annular grooves 16 and 17 and underneath the side faces of the gear wheels. The clearance space of the shafts 7 and 8 in the bores 5 and 6 must thus be so constricted that sufliicient pressure oil flows to the gear wheels.

The purpose of the longitudinal bores 20 and 21 is also to balance or compensate for the differences in pressure on the ends of the shafts 7 and 8, as such differences would tend to retard the automatic adjustment or self-centering of the gear wheels.

What we claim is:

1. A gear pump comprising a pump housing having a chamber provided with spaced end walls, said end walls having cylindrical bearing bores extending from the chamber, meshing gear wheels positioned in the chamber and being of an axial length slightly less than the axial length of the chamber to provide clearance spaces between the sides of the gear wheels and the end walls of the chamber, cylindrical gear shafts mounted for rotation and axial displacement in the bores and on which the gear wheels are mounted, the chamber being provided on its end walls at both sides of the gear wheels symmetrically with grooves connecting the region in which the gear wheels are in mesh simultaneously with two grooves, each of the latter of which surrounds a bearing bore with its inner edge at least near the bore and its outer edge having a sufficient distance from the grounds of the tooth spaces to provide a sealing rim between the groove and the tooth spaces, the surfaces of the bores and the shafts being entirely cylindrical and uninterrupted and the clearance between the shafts and the bores being as small as possible so that the fluid medium entrapped at the intermeshing point of the gear wheels disperses constantly and symmetrically into the clearance spaces on both sides of the gear wheels to provide a cushion between the gear wheels and the end Walls of the chamber so as to retain the gear wheels in a substantially central axial position in the chamber.

2. A gear pump comprising a pump housing having a chamber provided with spaced end walls, said end walls having cylindrical bearing bores extending from the chamber, meshing gear wheels positioned in the chamber and being of an axial length slightly less than the axial length of the chamber to provide clearance spaces between the sides of the gear wheels and the end walls of the chamber, cylindrical gear shafts mounted for rotation and axial displacement in the bores and on which the gear wheels are mounted, the chamber being provided on its end walls at both sides of the gear wheels symmetrically with straight grooves connecting the region in which the gear wheels are in mesh simultaneously along the shortest distance line with two grooves, each of the latter of which surrounds a bearing bore with its inner edge at least near the bore and its outer edge having a sufficient distance from the grounds of the tooth spaces to provide a sealing rim between the groove and the tooth spaces, the surfaces of the bores and the shafts being entirely cylindrical and uninterrupted and the clearance between the shafts and the bores being as small as possible so that the fluid medium entrapped at the intermeshing point of the gear wheels disperses constantly and symmetrically into the clearance spaces on both sides of the gear wheels to provide a cushion between the gear Wheels and the end walls of the chamber so as to retain the gear wheels in a substantially axial position in the chamber.

References Cited in the file of this patent UNITED STATES PATENTS Wood July 9, 1918 1,372,576 Tullmann Mar. 22, 1921 1,620,261 Kennedy Mar. 8, 1927 1,634,023 Davison June 28, 1927 1,641,486 Heil Sept. 6, 1927 1,682,842 Hamer Sept. 4, 1928 1,706,829 Thomson Mar. 26, 1929 1,972,271 McIntyre Sept. 4, 1934 2,202,913 Johnson June 4, 1940 2,316,565 Collier Apr. 13, 1943 2,391,072 Pugh Dec. 18, 1945 2,471,149 Girz May 24, 1949 2,487,732 Schanzlin Nov. 8, 1949 2,498,911 Chittenden Feb. 28, 1950 2,626,570 Armington et al. Jan. 27, 1953 

